1. Field of the Invention
The present invention relates to a vacuum pump and, more particularly, to a multi-stage vacuum pump, which has a small outer diameter and reduced volume and weight and, which is inexpensive to manufacture.
2. Description of Related Art
Regular equipment for clean manufacturing process, for example, equipment for depositing process, etching process, ion implanting process in semiconductor manufacturing commonly use a vacuum system to provide a proper vacuum environment for operation.
In the aforesaid vacuum system, a vacuum pump is used to achieve the desired vacuum effect. Therefore, the quality of the vacuum pump determines the achievement of the vacuum system.
FIG. 1 is a sectional view of a multi-stage vacuum pump according to the prior art. According to this design, the multi-stage vacuum pump 9 is comprised of a plurality of casings 911˜915 and a plurality of partition plates 921˜924 axially alternatively arranged in a stack. FIG. 2 is an exploded view of one pump unit of the multi-stage vacuum pump 9. FIG. 3 is a sectional view of the assembly of FIG. 2. As illustrated, the pump unit comprises a casing 914, which defines a compression chamber 904 and an air path 900 extended around the compression chamber 904 and adapted to guide compressed air from the compression chamber 904 to a next compression chamber 903 (see FIG. 1) for a next compression operation, a partition plate 924 covering the compression chamber 904, two shafts 931 and 932 arranged in parallel and extended through the partition plate 924, and two rotors 933 and 934 respectively formed integral with the shafts 931 and 932 and meshed together in the compression chamber 904 and adapted to compress air in the compression chamber 904.
As illustrated in FIGS. 2 and 3, the air path 900 is formed in the wall thickness of the casing 914 around the compression chamber 904. The presence of the air path 900 greatly increases the diameter and volume of the casing 914. Due to this drawback, the size and weight of the multi-stage vacuum pump 9 cannot be reduced to the desired level.
Therefore, it is desirable to provide a multi-stage vacuum pump, which eliminates the aforesaid drawbacks.